The long-term goal of our research is to improve systemic delivery of drugs with limited oral bioavailability due to extensive first-pass elimination by means of site-specific vaginal administration in the female. The central hypothesis of the present proposal is that progesterone regulates functional expression of P-glycoprotein (P-gp) in the vaginal mucosa leading to variable drug efflux. As a consequence, maximum vaginal bioavailability of P-gp substrates is restricted to a defined time window during the menstrual cycle. The MDR1 gene product P-gp is a prototype of membrane efflux systems that limit transcellular transport of drug molecules with broad specificity at strategic epithelial and endothelial membrane barriers, including the gastrointestinal mucosa. Thus, there are three specific aims proposed: (l) To test the hypothesis that progesterone regulates P-gp expression in human vaginal mucosa in vivo and in vitro. (2) To determine whether P-gp efflux activity in human vaginal epithelial cells in vitro is regulated by progesterone. (3) To test the prediction that progesterone regulates P-gp expression at the transcriptional level. Northern blot analysis will be conducted to quantify mRNA of P-gp in biopsies of human vaginal mucosa collected during the menstrual cycle as well as progesterone-treated immortalized human vaginal epithelial cells. Protein expression in response to cyclic hormonal changes will be determined by immunoblot analysis. Functional activity of P-gp will be assessed in vitro using intracellular accumulation of the P-gp substrate digoxin. Experiments will be designed to determine whether progesterone-induced changes in digoxin accumulation satisfy established criteria for P-gp-mediated efflux, including directionality, dependency on energy and substrate concentration, and sensitivity to selective inhibition. Finally, promoter/reporter constructs will be prepared to determine DNA sequences in the upstream region of the MDR1 gene that facilitate progesterone signaling. The significance of this research is that it will set the stage for future mechanistic studies to elucidate the interplay of female reproductive hormones in the regulation of vaginal P-gp. From the drug delivery point of view, the results may be applicable to determine an optimum time window during the menstrual cycle for effective vaginal delivery of P-gp substrates in order to maximize systemic bioavailability. [unreadable] [unreadable]